Fabrication of integrated circuits frequently require selectively deposition of metal layers upon semiconductors. One of the problems associated with such metal layers is the tendency of electromigration of the metal, which may adversely affect the integrity of semiconductor devices incorporation the metal layers, particularly where the metal layers form part of an integrated circuit. Copper (Cu) is one of the promising metals used for such metal layers for next generation ultra-large scale integration (ULSI) metallization due to Cu's low resistivity and relatively high electomigration resistance.
It has been reported that the copper electomigration can be improved by alloying Cu with, for example, zirconium (Zr) or tin (Sn). It has been reported that copper doped with zirconium or tin has one order of electromigration life time. "One order of electromigration life time" means that CuZr and CuSn alloys have a electromigration reduction that is a power of ten (10) times better than non-doped copper. This is because the Zr or Sn doping material segregates in the grain boundary and reduces the grain boundary diffusion. However, the conventional doping process for CuZr or CuSn alloys involve sputtering a Zr or Sn metal over Cu, or co-sputtering. For the most extensively used electrochemical deposition of Cu, such sputtering is not easy to apply. Also, doping copper with titanium (Ti), aluminum (Al), Zr or Sn increases the resistivity of Cu from 1.7 .mu.ohms-cm to between about 3 to 5 .mu.ohms-cm. In order to reduce this increased resistivity to about 2.3 .mu.ohms-cm, a subsequent high temperature annealing step (around 500.degree. C.) is necessary. However such a high temperature annealing is not allowed in the Cu backend process as it may degrade the doped layer(s) and any aluminum (Al) layers.
U.S. Pat. No. 5,789,320 to Andricacos et al. describes plating of noble metal electrodes for DRAM and FRAM. Noble metals are plated on a preexisting seed layer and may be spatially selective or non selective. A diamond-like carbon mask can be used in the plating process. A self-aligned process is also described for selectively coating insulators in a through-mask process.
U.S. Pat. No. 4,950,615 to Basol et al. describes a technique for forming thin films of Group IIB metal (zinc (Zn), cadmium (Cd) or mercury(Hg))--telluride (Te), such as Cd.sub.x Zn.sub.1-x Te (0.ltoreq.x.ltoreq.1) on a substrate. A technique is also described for doping this material by chemically forming a thin layer of a dopant on the surface of the unreacted elements and then heating the elements along with the layer of dopant, as well as a method of fabricating a thin film photovoltaic cell.
U.S. Pat. No. 5,681,779 to Pasch et al. describes a method of doping metal layers on integrated circuits to provide electromigration resistance and integrated circuits having metal alloy interconnects characterized by being resistant to electromigration. Copper doped aluminum is preferred although tungsten (W) doped copper is also disclosed. The dopant is applied subsequent to patterning and etching of the integrated circuit structure and the structure is then heated at a temperature (preferably 350.degree. C. to 450.degree. C.) sufficient to uniformly diffuse the second metal dopant through the bulk of the patterned, first conductive metal film.